Alcohols

Foundation in Science Mahsa University College

Chem 2Topic: Alcohol

Prepared by Mr. Daniel Philip

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An alcohol consists of a carbon chain with a hydroxy group (-OH) attached

Alcohols

Methanol

Ethanol

Propanol

Phenol

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1. Naming and Drawing molecules

Nomenclature of Alcohols

a) Alcohols are named by dropping the e ending of the parent alkane and replacing with ol. The –OH group can also be named as a substituent using the group name, hydroxy.

b) Still another nomenclature involves naming the alkyl group followed by a space and the word alcohol

General formula of alcohols CnH2n+2O

First member is Methanola) Displayed formula is H  

|  H-C-O-H |   H 

b) Systematic name: methanol(from : methan + ol)c) Structural formula - CH3OH d) Molecular formula CH4O

Names and Structural formula of common alcohols

Examples:CH3OH Methanol CH3CH2OH Ethanol

CH3CH2CH2OH is calledpropan-1-ol or 1-propanol

CH3CH(OH)CH3 is calledpropan-2-ol or 2-propanol

if more than one hydroxyl is present, the prefixes di-, tri-, tetra-... are used the terminal "e" is retained on the parent alkane name.

CH2OHCH(OH)CH2OH

Common name is Glycerol and systematic name is 1,2,3-propanetriol.

Exercise 1

Give the displayed formula, structural formula, molecular formula and empirical formula of the following alcohols

a) 1-butanol

b) 2-butanol

c) 2-methyl-1-propanol

d) 2-methyl-2-propanol

Name the following molecules:

Alcohols may be classified as - Primary - Secondary - TertiaryDepending on whether the carbon atom that is attached to the –OH group is surrounded by one, two or three other carbon atoms

Alcohol Classification

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Primary AlcoholsA primary alcohol is bonded to carbon atom that is bonded also to one or no carbon atom carbon atom.

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A secondary alcohol is attached to a carbon atom that is bonded also to 2 carbon atoms.

Secondary Alcohols

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Tertiary Alcohols

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Polyhydroxy alcoholsAlcohols that have more than one OH group are known as polyhydroxyl alcohols. Two examples are shown below

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Name and classify the following alcohols.

• 2-butanol (Secondary)

• 2-propene-1-ol (Primary)

• 2-methyl-1-butanol (Primary)

• 2-methyl-2-butanol (Tertiary)

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The physical properties of alcohols are similar to those of both water and hydrocarbons

The shorter chain alcohols such as methanol and ethanol are similar to water, in general they

-- have higher boiling points than hydrocarbons but lower than water-- dissolve in water to some degree-- are more polar than hydrocarbons but less polar than water

Properties of Alcohols

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Alcohols are polar molecules

Reactivity: • The image shows the electrostatic potential for methanol. 

The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 

• The alcohol O atom are a region of high electron density (red) due to the lone pairs.  

3. Physical properties

• 1. Boiling point is higher than hydrocarbon. (Due to intermolecular H-bond)

• 2. Spirituous odour with burning taste.• 3. Short chain alcohols, up till 4 carbon

atoms are soluble in water.

Extra info: Phenol (at room temperature) is colourless liquid but tinged with pink oxidation product. It is moderately soluble in water. It is corrosive.

Exercise

1. Explain why ethanol liquid is soluble in water but ethane gas isn’t soluble in water. 4marks

2. Explain why the boiling point of ethanol is greater than the boiling point of ethane. 4marks

Reactions of Alcohols

Alcohols undergo several types of reactions including:

OxidationDehydrationReactions with active metalsEsterificationSubstitution

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4. Chemical reactions of Alcohols

4.1 Alcohol with alkali metals → alkoxide (strong base!)

2 Na + 2 CH3OH → H2(g) + 2 CH3O- + 2 Na+

(sodium methoxide)

4.2. Alcohol substitution

CH3CH2CH2OH + HCl → CH3CH2CH2Cl + H2O

CH3CH2OH + PCl5 CH3CH2Cl + HCl + POCl3

4.3. Alcohol dehydration

CH3-CH2-OH → CH2=CH2 + H2O

Chemical reactions of Alcohols

4.4 Alcohol oxidation (burning) * primary alcohols → aldehydes* secondary alcohols → ketones* tertiary alcohols → no reaction

4.5 Alcohol with caboxylic acid for Esterification reaction

alcohol + acid → ester + H20

4.4 OxidationAlcohols are oxidized to alkanals (aldehydes) or alkanones (ketones) and even carboxylic acids.

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Primary Alcohols are Oxidized to Alkanals/Aldehyde

The most common oxidizing agents are acidic KMnO4

soultion or , acidic K2Cr2O7 or even oxygen from the air(very very slow). The mechanisms of such reactions are usually complex

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Secondary Alcohols are oxidized to Alkanones/Ketones

Example

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Tertiary Alcohols are not easily oxidized

There is no hydrogen attached to the tertiary carbon. It is not possible for a carbonyl group on the tertiary carbon to be oxidixed.

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Tertiary Alcohols are not easily oxidized

Furthermore the large R groups on the tertiary carbon, prevent reacting groups. Hence tertiary alcohols are rather unreactive.

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4.4. Oxidation

CR O H

H

H

+ [O] R C H

O

+ H2O

excess [O]R C

O

OH

Aldehyde / Alkanal Carboxylic acid

CR O H

R'

H

+ [O] R C R'

O

Ketone

Primary alcohol

Secondary alcohol

Common O.A. :K2Cr2O7/ H+, KMnO4/ H+

Oxidizing agents are acidified KMnO4 or acidified K2Cr2O7

Primary alcohol with acidic oxidizing agent solution, distilled, gives aldehyde

Primary alcohol with acidic oxidizing agent solution, reflux boiling, gives carboxylic acid

Secondary alcohol with acidic oxidizing agent solution, reflux boiling, gives ketone

Observation:a) acidified KMnO4 solution/acidified manganate(VII)

solution :

Purple to Colourless or purple is decolourised

Or

b) acidified K2CrO7 solution/acidified dichromate(VI) solution :

Orange to Green

Exercise

Draw the displayed structure of the organic product formed, if any when the following alcohol was heated with acidified KMnO4 solution, reflux (boiling)

a) Methanolb) Ethanolc) 1-propanold) 2-propanole) 1-butanolf) 2-butanolg) 2-methyl-1-propanolh) 2-methyl-2-propanol

Draw the displayed structure of the organic product formed, if any when the following alcohol was mixed with acidified KMnO4 solution and the product is distilled off

a) Methanolb) Ethanolc) 1-propanold) 1-butanole) 2-methyl-1-propanol

4.3 DehydrationMany alcohols undergo intramolecular dehydration, removing water to form alkenes.

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4.3 Dehydration

Definition: removal of water from a molecule.Extra info: H and OH are removed from two

adjacent carbons.Reagent and conditions:Dehydrating agentsCon H2SO4, heatCon H3PO4, heatSolid SiO2, heatSolid Al2O3, heatSolid ceramic or solid pumice, heat

Exercise

Write an equation and then give the displayed structure of the organic product formed, if any when the following alcohol was heated with con.H2SO4 and heated(warm/boil or reflux boiling)

a) Ethanolb) 1-propanolc) 2-propanold) 1-butanole) 2-butanolf) 2-methyl-1-propanolg) 2-methyl-2-propanol

4.1 Reactions with Metals• Alcohols are far less acidic than water but they

react with highly reactive metals such as potassium and sodium.

• The metal replaces the hydrogen atom in the alcohol group forming a salt and hydrogen gas

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Note that the reaction between Na, sodium solid and alcohol at room temperature releases colourless gas of H2. This indicates the presence of OH hydroxy group in alcohols.

Quick exercise

Write an equation for reaction between Sodium metal at r.t. with

a) Methanol

b) Ethanol

c) 1-propanol

d) 2-propanol

EsterificationAn alcohol reacts with an alkanoic acid to form an ester and water.

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Write an equation and then give the displayed structure of the organic product formed, if any when the following alcohol was heated with ethanoic acid with drops of con.H2SO4 and heated(warm/boil or reflux boiling)

a) Methanolb) Ethanolc) 1-propanold) 2-propanole) 1-butanolf) 2-butanolg) 2-methyl-1-propanolh) 2-methyl-2-propanol

ExerciseEthanol undergoes the following reactions:Reaction 1: Ethanol EtheneReaction 2: Ethanol EthanalReaction 3: Ethanol Ethanoic acidReaction 4: Ethanol CH3CH2ONaReaction 5: Ethanol CH3CH2CO2CH2CH3Reaction 6 : Ethanol to CH3CH2Cl

a) Name the type of organic reaction in reaction labelled as:1:…………………………………2 :…………………………………3 :…………………………………4 :…………………………………5 :…………………………………6:…………………………………

Ethanol undergoes the following reactions:Reaction 1: Ethanol EtheneReaction 2: Ethanol EthanalReaction 3: Ethanol Ethanoic acidReaction 4: Ethanol CH3CH2ONaReaction 5: Ethanol CH3CH2CO2CH2CH3Reaction 6 : Ethanol to CH3CH2Cl

b) Give the reagents and conditions for reaction labelled as1:…………………………………2 :…………………………………3 :…………………………………4 :…………………………………5 :…………………………………6:………………………………….

Ethanol undergoes the following reactions:Reaction 1: Ethanol EtheneReaction 2: Ethanol EthanalReaction 3: Ethanol Ethanoic acidReaction 4: Ethanol CH3CH2ONaReaction 5: Ethanol CH3CH2CO2CH2CH3Reaction 6 : Ethanol to CH3CH2Cl

C) Give the observation for reaction labelled as

1:…………………………………2 :…………………………………3 :…………………………………4 :…………………………………5 :…………………………………6: ……………………………………..

Ethanol undergoes the following reactions:Reaction 1: Ethanol EtheneReaction 2: Ethanol EthanalReaction 3: Ethanol Ethanoic acidReaction 4: Ethanol CH3CH2ONaReaction 5: Ethanol CH3CH2CO2CH2CH3Reaction 6 : Ethanol to CH3CH2Cld) Name the organic products of reaction labelled as4:………………………..5:………………………..6:………………………..

Ethanol undergoes the following reactions:Reaction 1: Ethanol EtheneReaction 2: Ethanol EthanalReaction 3: Ethanol Ethanoic acidReaction 4: Ethanol CH3CH2ONaReaction 5: Ethanol CH3CH2CO2CH2CH3Reaction 6 : Ethanol to CH3CH2Cle) Give the displayed formula of organic prodct formed from

reaction labelled as 1:2:3: